(a) Field of the Invention
The present invention relates to methods for the identification of coded labels carried by articles, for the purpose of starting an operation corresponding to the code detected, or for the purpose of a subsequent selective treatment of these articles. Throughout the following text, the term "label" will be understood in a very broad sense which applies both to the case where the elements used for coding are carried by a so-called label, which is itself fixed to or enclosed in the article, and to the case where the coding elements are carried directly by the article, for example by being glued thereto.
(b) Prior Art
The Assignees of the present invention have previously filed patent applications relating to methods for coding and identifying magnetically coded labels. In these applications, a magnetic tape is passed through a detection zone having at least one sensor, each sensor comprising an exciter coil supplied with an alternating current in order to create an alternating magnetic field and a detector coil which is tuned so that no signal is detected in the absence of a magnetic body near the sensor.
U.S. Pat. No. 4,134,538 discloses means for coding which uses a single magnetic element, the code being detected by measuring the amplitude of the detected signal, which can be altered by varying the height or area of the magnetic element.
Alternatively, several magnetic elements can be used which are made of alloys having different hysteresis loops. The coding is then achieved by placing the elements on the labels, so that the overall signal created due to the different hysteresis loops reproduces signals characteristic of each element in the same order as the elements are disposed on the label. Detection is achieved by locating the relative positions of the signals and by measuring the amplitude of each of these signals.